Multi-section stent

ABSTRACT

A stent includes a first stent section, a second stent section, and at least one connecting member. The connecting member has a first end attached to the first stent section, a second end attached to the second stent section and a physically separable portion.

This application is a continuation-in-part of U.S. Ser. No. 09/292,558,filed Apr. 15, 1999, now U.S. Pat. No. 6,258,117.

TECHNICAL FIELD

The present invention relates to medical prostheses and, moreparticularly, to intraluminal medical stents.

BACKGROUND

Medical stents are used within the body to restore or maintain thepatency of a body lumen. Blood vessels, for example, can becomeobstructed due to plaque or tumors that restrict the passage of blood. Astent typically has a tubular structure defining an inner channel thataccommodates flow within the body lumen. The outer walls of the stentengage the inner walls of the body lumen. Positioning of a stent withinan affected area can help prevent further occlusion of the body lumenand permit continued flow.

A stent typically is deployed by percutaneous insertion of a catheter orguide wire that carries the stent. The stent ordinarily has anexpandable structure. Upon delivery to the desired site, the stent canbe expanded with a balloon mounted on the catheter. Alternatively, thestent may have a biased or elastic structure that is held within asheath or other restraint in a compressed state. The stent expandsvoluntarily when the restraint is removed. In either case, the walls ofthe stent expand to engage the inner wall of the body lumen, andgenerally fix the stent in a desired position.

SUMMARY

The present invention is directed to a multi-section stent. The stentincorporates a connecting structure that permits the multiple sectionsto move relative to another, promoting flexibility and conformance ofthe stent to a body lumen. For deployment and positioning, theconnecting structure holds the stent sections substantially stationaryrelative to one another. Following deployment, however, the connectingstructure allows the multiple stent sections to move relative to oneanother.

The connecting structure can be made to separate or relax such that thestent sections are able to move relative to one another. The connectingstructure can be made to separate or relax by the use of a material thatbreaks or degrades. Movement of the stent sections may refer to axialmovement, lateral movement, tilting, pivoting, rotation, and the like,all of which promote flexibility of the overall stent structure.

Movable stent sections enable flexure of the stent upon deploymentwithin a body lumen. This flexing structure allows better conformance ofthe stent to the shape of the body lumen, and exerts less overallpressure against the lumen wall, reducing the potential for trauma.Following separation or relaxation of the connecting structure, themultiple stent sections may be completely detached from one another.Alternatively, the stent sections may remain partially connected in amanner that allows substantial independent movement.

The connecting structure can be manufactured to separate, e.g., bybreakage, tearing, rupture, etc., thereby disconnecting at leastportions of adjacent stent sections to allow increased flexibility.Alternatively, the separable connecting structure can be made from adegradable material that dissolves or otherwise degrades within the bodylumen. As a further alternative, the connecting structure may connectthe stent sections in a non-rigid manner, allowing movement whileretaining interconnection between the stent sections. In any of theabove cases, adjacent stent sections become more movable relative to oneanother, allowing the stent to flex and adapt to the body lumen. Each ofthe individual stent sections may settle into a substantially fixedposition, however, and heal into the luminal wall.

A separable connecting structure can be made responsive to intra-luminalforces or external forces applied upon deployment. To promote separationby breakage, a continuous stent structure can be weakened, e.g., bythinning, perforation, scribing, or pre-stressing, at selected intervalsalong the length of the stent. Alternatively, discrete connectingmembers can be formed between stent sections to provide a series ofconnected stent sections. The connecting members are manufactured toseparate under intraluminal forces, thereby disconnecting the stentsections. To promote early separation or breakage, the deploymenttechnique may involve forcibly breaking at least some of the connectingmembers. In many cases, however, gradual separation or breakage underintraluminal forces will be sufficient.

A connecting structure incorporating a degradable material can beselected to dissolve within the body fluids present within the bodylumen in which the stent is positioned. Early degradation can bepromoted by pretreating the material, e.g., with a solvent, just priorto deployment. Also, an agent may be introduced into the body toaccelerate degradation. If the connecting structure comprises a collagencoating, for example, an enzyme dosage can be administered to thepatient to promote degradation. Gradual degradation will be sufficientin most applications, however, simplifying preparation. With degradablematerials, therapeutic substances can be added for release into the bodylumen as the materials degrade.

As an alternative, the stent can be covered with a brittle or degradablelaminating coat that covers at least a portion of the stent, forming ahousing for the stent sections. This housing can provide a substantiallyrigid but separable interconnection of the stent sections. Upondeployment, the housing breaks or degrades to permit greater flexibilityamong the stent sections. Another alternative is the use of a housing inthe form of a breakable or degradable netting or cage that holds thesections together. Upon deployment, the netting or cage can be made tobreak or degrade, and thereby release the stent sections relative to oneanother.

Separable connecting portions, whether degradable or breakable, can beselected and manufactured to minimize the risk of releasing largerparticles or fragments into the body lumen that could lead to embolismor other serious problems. The stent sections may be completelyseparated, i.e., disconnected, following breakage of the connectingstructure, forming a series of discrete stent sections that extend alongthe body lumen. Alternatively, the stent sections may remain partiallyconnected, but still provide improved flexibility. For example, materialjoining adjacent stent sections may remain partially intact to allowflexibility but limit movement.

As further alternatives, the stent sections can be connected withinterlocking links, such as loops or chain-links, that allow the stentsections to move, but serve to restrict the overall extent of movement.In some embodiments, the interlocking links may overlap, with degradableor breakable material filling the overlap area to hold adjacent stentsections in a substantially fixed manner and at a substantially fixeddistance relative to one another. Following degradation or breakage ofthe material in the overlap, the links allow at least some degree ofmovement of the stent sections. In this manner, the length of the stentmay increase following deployment, and occupy a greater extent withinthe body lumen.

In one embodiment, the present invention provides a stent comprising afirst stent section, a second stent section, and a connecting structurethat connects the first and second stent sections, the connectingstructure allowing the first and second stent sections to move relativeto one another upon deployment of the stent within a body lumen.

In another embodiment, the present invention provides a stent comprisinga first stent section, a second stent section, a first link extendingfrom the first stent section, a second link extending from the secondstent section, wherein the first and second links interlock and definean overlap region, and a material formed in the overlap region to holdthe first and second stent sections in a substantially fixedrelationship, wherein the material is separable upon deployment of thestent within a body lumen, thereby enabling the first and second stentsections to move relative to one another.

In a further embodiment, the present invention provides a stentcomprising a first stent section, a second stent section, a first linkthat interlocks with a second link in the first stent section and athird link in the second stent sections, thereby connecting the firstand second stent sections, wherein the first link defines a firstoverlap region with the second link and a second overlap region with thethird link, and a material formed in the first and second overlapregions to hold the first and second stent sections in a substantiallyfixed relationship, wherein the material is separable upon deployment ofthe stent within a body lumen, thereby enabling the first and secondstent sections to move relative to one another.

In an added embodiment, the present invention provides a stentcomprising a first stent section, a second stent section, and aconnecting member that connects the first and second stent sections, theconnecting member holding the first and second stent sections in asubstantially fixed relationship, wherein the connecting member relaxesthe connection between the first and second stent sections followingdeployment of the stent within a body lumen, thereby enabling flexure ofthe stent.

In another embodiment, the present invention provides a stent comprisinga first stent section including a first spring coil, a second stentsection including a second spring coil, a first spring arm extendingfrom the first stent section, a second spring arm extending from thesecond stent section, and a material that connects the first and secondspring arms, the material being breakable, thereby at least partiallydisconnecting the first and second stent sections and allowing the firstand second stent sections to move relative to one another.

In a further embodiment, the present invention provides a stentcomprising a first stent section, a second stent section, and a housingthat encloses at least portions of the first and second stent sections,wherein the housing is breakable upon deployment, thereby allowing thestent sections to move relative to one another following degradation ofthe housing.

In another embodiment, the present invention provides a stent comprisinga first stent section, a second stent section, and a housing thatencloses at least portions of the first and second stent sections,wherein the housing is degradable upon deployment, thereby allowing thestent sections to move relative to one another following degradation ofthe housing.

In another embodiment, the present invention provides a stent comprisinga first stent section, a second stent section, and at least oneconnecting member having a first end attached to the first stentsection, a second end attached to the second stent section and aphysically separable portion. The physically separable portion maycomprise at least one groove in the connecting member. The groove may beformed adjacent to the first end, or adjacent to the first end and thesecond end.

The connecting member of the stent may further include an angledportion. The angled portion may include a groove and the physicallyseparable portion may comprise the groove. The angle may be less than45°, between 45° and 135°, and/or between 135° and 180°.

The stent may include one, two, three, four, or more connecting members.If there are two connecting members, each connecting member may includea first end attached to the first stent section and a second endattached to the second stent section, and the first end of the firststent is adjacent to the first end of the second stent. The first end ofthe first connecting member and the first end of the second connectingmember may be separated by approximately 180°. The second end of thefirst connecting member and the second end of the second connectingmember may be separated by approximately 180°. In the stent, thephysically separable portion may separate during a deployment of thestent or after a deployment of the stent.

In another embodiment, the stent includes a first stent section, asecond stent section; and a pair of connecting members. The connectingmembers are positioned between the stent sections and connect the stentsections. Each connecting member is substantially coplanar over aportion of a length of the connecting member with the at least one stentsection and includes a first end attached to the first stent section, asecond end attached to the second stent section and a physicallyseparable portion.

In the stent, the physically separable portion of a first connectingmember may be configured to separate from the first stent section andthe physically separable portion of the second connecting member may beconfigured to separate from the second stent section, whereby the firstconnecting member is configured to reduce tumbling of the first stentsection and the second connecting member is configured to reducetumbling of the second stent section. The stent may be fabricated byelectron discharge machining.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are side views of a multi-section stent having aseparable connection structure incorporating v-shaped grooves;

FIG. 1C is a perspective view of a multi-section stent as shown in FIG.1A;

FIGS. 2A and 2B are side views of a multi-section stent having aseparable connection structure incorporating square grooves;

FIGS. 3A and 3B are side views of a multi-section stent having aseparable connection structure incorporating perforations;

FIGS. 4A and 4B are side views of a multi-section stent having aseparable connection structure incorporating discrete breakableconnecting members;

FIG. 4C is a perspective view of a multi-section stent as shown in FIG.4A;

FIGS. 5A and 5B are side views of a multi-section stent having aseparable connection structure incorporating discrete breakableconnecting members;

FIGS. 6A, 6B, and 6C are side views of a multi-section stent having aseparable connection structure incorporating interlocking links;

FIGS. 7A and 7B are side views of another multi-section stent having aseparable connection structure incorporating interlocking links;

FIGS. 8A and 8B are side views of a multi-section stent having a springcoil structure with separable connecting members;

FIGS. 9A and 9B are perspective side views of a multi-section stent withconnecting loops;

FIGS. 10A and 10C are side views of a multi-section stent with adegradable housing;

FIG. 10B is an end view of the multi-section stent of FIG. 10A;

FIG. 11A is a perspective side view of a multi-sectional stent;

FIGS. 11B and C are an end view and an enlarged side view of themulti-sectional stent of FIG. 11A;

FIG. 12 is a side view of a multi-sectional stent having an angledconnecting member in which the angle is relatively small;

FIG. 13 is a side view of the multi-sectional stent of FIG. 12 deployedin an artery;

FIG. 14 is a side view of a multi-sectional stent having an angledconnecting member in which the angle is relatively large;

FIG. 15 is a side view of the multi-sectional stent of FIG. 14 deployedin an artery;

FIG. 16 is a side view of a multi-sectional stent having an angledconnecting member;

FIG. 17 is a side view of a multi-sectional stent deployed in a tortuousartery;

FIG. 18 is a side view of a multi-sectional stent deployed in anon-tortuous artery having severe lesions;

FIG. 19 is a side view of a multi-sectional stent having one connectingmember;

FIG. 20 is a side view of a multi-sectional stent having two connectingmembers;

FIG. 21 is a perspective view of a multi-sectional stent having angledconnecting members attached at offset positions;

FIG. 22 is a perspective view of a multi-sectional stent having anangled connecting member attached at offset positions;

FIGS. 23 and 24 are perspective views of a catheter having a sheath fordeploying a stent fabricated from a shape memory material;

FIGS. 25-27 are perspective views of separated stent sections havingattached connecting members; and

FIGS. 28-31 are perspective view of the steps of forming amulti-sectional stent using electron discharge machining (“EDM”).

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIGS. 1A and 1B are side views of a multi-section stent 10 having aseparable connection structure that facilitates enhanced flexibility.FIG. 1C is a perspective view of multi-section stent 10. In the exampleof FIGS. 1A-1C, multi-section stent 10 includes five stent sections 12,14, 16, 18, 20. Stent 10 may include a lesser or greater number of stentsections, however, depending on the application. For example, stent 10may include as few as two stent sections in some applications. Eachstent section 12, 14, 16, 18, 20 has a ring-like structure with an innerwall 22, an outer wall 24, and a central aperture 26. Stent sections 12,14, 16, 18, 20 are arranged coaxially and in series to form thelongitudinal extent of stent 10. Stent sections 12, 14, 16, 18, 20define an inner channel 28, indicated by dashed lines 30, 32 in FIG. 1A,that extends along the length of stent 10.

Upon deployment, inner channel 28 is sized to accommodate flow within abody lumen. Outer wall 24 of each stent section 12, 14, 16, 18, 20 issized, upon deployment, to engage the inner surface of the body lumen,and thereby resist further occlusion. In this manner, stent 10 iseffective in restoring or maintaining the patency of a body lumen, suchas a blood vessel. The dimensions of stent sections 12, 14, 16, 18, 20may vary depending on the application. In many applications, thediameters of inner wall 22 and outer wall 24 will be the same for allstent sections 12, 14, 16, 18, 20. Similarly, each of stent sections 12,14, 16, 28, 20 may have the same axial length. For some applications,however, variation in the inner and outer diameters and lengths ofindividual stent sections 12, 14, 16, 18, 20 is conceivable.

Connecting members 34, 36, 38, 40 connect adjacent stent sections 12,14, 16, 18, 20 to one another in a substantially fixed relationship.Connecting member 34, for example, forms a connection between adjacentstent sections 12 and 14. In the example shown in FIGS. 1A-1C,connecting members 34, 36, 38, 40 are not discrete components. Instead,connecting members 34, 36, 38, 40 are formed integrally with the body ofstent 10. Stent 10 can be formed as a continuous structure, e.g., bymolding, casting, lamination, deposition, or other known manufacturingprocesses. Each connecting member 34, 36, 38, 40 can be formed bythinning, perforating, pre-stressing or otherwise weakening portions ofstent 10 between adjacent stent sections 12, 14, 16, 18, 20.

As shown in FIG. 1A, for example, connecting members 28, 30, 32, 34 maytake the form of v-shaped grooves 42, 44, 46, 48 that are spaced axiallyalong the length of stent 10 between adjacent stent sections 12, 14, 16,18, 20. Each groove 42, 44, 46, 48 extends circumferentially about stent10. The minimum diameter of each groove 42, 44, 46, 48 is sized largerthan that of inner channel 22, but significantly smaller than that ofstent 10. In this manner, grooves 42, 44, 46, 48 produce a thinned areathat serves to weaken, and promote breakage of, stent 10 at selectedpositions. In particular, grooves 42, 44, 46, 48 preferably are designedto promote breakage of stent 10 in response to intra-luminal forces,either immediately following deployment or over an extended period oftime. Upon breakage, stent sections 12, 14, 16, 18, 20 are separablefrom one another.

Stent sections 12, 14, 16, 18, 20 can be coated or impregnated withtherapeutic materials such as heparin. The materials can be selected todissolve upon deployment within the body lumen. For example, thematerials can be incorporated in body-soluble sugars that dissolvewithin a blood vessel. Alternatively, the materials can be dissolved inresponse to introduction of a dissolving agent into the body. Collagencoatings, for example, can be selected to dissolve upon ingestion orinjection of a particular enzyme dosage. As a further alternative,temperature-sensitive materials can be selected for coating orimpregnation in stent sections 12, 14, 16, 18, 20. When heated to bodytemperature following deployment, the materials can dissolve to deliverdesired therapeutic materials. Also, breakage could be further promotedby coating stent sections 12, 14, 16, 18, 20 with a material that swellsupon absorption of fluid within the body lumen. Such a material could beselected to become more rigid upon absorption, thereby exerting a forceagainst connecting members 34, 36, 38, 40 to induce breakage. Stent 10can be constructed from a variety of different materials. Examplesinclude metals such as gold, silver, platinum, stainless steel,tantalum, titanium, shape-memory alloys such as nickel-titanium alloysreferred to as Nitinol, as well as synthetic polymers and biologicalmaterials such as natural fibrin. Such materials can be selected orcoated to provide radio-opacity, if desired. Nitinol may be particularlyadvantageous in light of its memory properties. With Nitinol, stent 10can be initially formed with a given configuration, and then deployed ina substantially flexible state. Stent 10 can be processed to provideconnecting members 34, 36, 38, 40, which present weakened areas of thestent body. Upon deployment, the Nitinol can be heated, e.g.,electrically or by exposure to body temperature, and thereby transformedto a more rigid state. In the process of transformation to a rigidstate, the Nitinol exerts a force that promotes breakage of connectingmembers 34, 36, 38, 40.

In some embodiments, stent 10 can be formed by processing asubstantially continuous starting material to provide connecting members34, 36, 38, 40.

A substantially continuous, material can be formed by molding orcasting. Grooves 42, 44, 46, 48 can be formed in initial manufacture orby subsequent processing. If stent 10 is formed by molding or casting,for example, grooves 42, 44, 46, 48 can be made during stent formation.Alternatively, the molding or casting operation may merely provide ablank for further processing. In this case, grooves 42, 44, 46, 48 canbe formed, for example, by mechanical scribing, laser etching,chemically etching, or mechanical milling or lathing the stent to formthe groove. As a further option, grooves 42, 44, 46, 48 could bethermally stamped or embossed, particularly if stent 10 is formed from apolymeric material. To further promote breakage, a series ofperforations could be formed along grooves 42, 44, 46,48. In any event,grooves 42, 44, 46, 48 should be formed at a depth sufficient to promotebreakage over time, but retain enough thickness to keep stent 10substantially intact during deployment. Thus, determination of the depthof grooves 42, 44, 46, 48 may require a trade-off between ease ofbreakage and structural integrity during deployment.

The depths of grooves 42, 44, 46, 48, i.e., the degree of thinning ofstent 10, can be the same. Stent sections 12, 14, 16, 18, 20 may besubject to different stresses due to their relative positioning alongthe length of stent 10, and the contour of the target site within thebody lumen. As a result, some of connecting members 34, 36, 38, 40 maybreak more easily than others. Accordingly, for some applications, itmay be desirable to form grooves 42, 44, 46, 48 with different depths toproduce more uniform breakage characteristics despite different stressesexisting at each connecting member 34, 36, 38, 40. Alternatively, othermethods, such as perforation, pre-stressing, etching, scribing, milling,or lathing, may be used to weaken individual connecting members 34, 36,38, 40 in a differential manner. Uniform breakage may be desirable forsome applications, but does not imply that connecting members 34, 36,38, 40 need to break at precisely the same time.

Upon breakage of stent 10 along grooves 42, 44, 46, 48, as shown in FIG.1B, the adjacent stent sections 12, 14, 16, 18, 20 are disconnected andseparate from one another. The disconnected stent sections 12, 14, 16,18, 20 remain positioned proximate one another within the body lumen,but are able to move independently. Consequently, stent 10 maintains thepatency of the body lumen while affording greater flexibility. Inparticular, depending on the contour and conditions of the target site,the disconnected stent sections 12, 14, 16, 18, 20 may be able to pivot,tilt, rotate, and move longitudinally within the body lumen relative toone another. Instead of presenting a rigid tube, stent 10 is better ableto conform to the shape of the lumen.

Stent 10 ordinarily will be sized or biased such that the inner wall ofthe body lumen exerts significant force radially inward against outerwall 24. This radial force will tend to restrain stent sections 12, 14,16, 18, 20 against excessive longitudinal movement. Given the radialforce, outer wall 24 of each stent section 12, 14, 16, 18, 20 shouldhave a surface area sufficient to prevent axial “tumbling” of the stentsection, i.e, a collapse such that the circular cross-section of stentsection moves away from a perpendicular position relative to the bodylumen wall. If a stent section 12, 14, 16, 18, 20 is extremely short inlength, relative to the longitudinal extent of the body lumen, tumblingcan be a problem. With sufficient length, interaction between outer wall24 and the inner wall of the body lumen will tend to anchor stentsections 12, 14, 16, 18, 20 against excessive movement. Eventually,stent sections 12, 14, 16, 18, 20 will settle into a generallystationary position and heal into the wall of the body lumen.

A separable connecting structure, as described herein, can be applied toa variety of different stent structures. Stent 10 can be fabricated froman elastomeric material or spring biased, for example, to allowcompression for deployment. Instead of having a solid, or substantiallycontinuous body, stent 10 can be fabricated by wrapping a sinusoidallyshaped wire in a series of turns about a form to provide a tube-likeshape. Adjacent wire turns can be partially cut or otherwise weakened topromote breakage at connecting members 34, 36, 38, 40. Upon release froma delivery catheter, sleeve, or other restraint, stent 10 is able tovoluntarily expand radially outward to fill the body lumen. Stents ofthis type are often referred to as self-expandable.

As an alternative, stent 10 can have an assisted expansion structure.Expansion can be assisted, for example, by inflating a balloon disposedwithin the stent. Self-expandable and balloon-expandable stentstructures are well known in the art. Optionally, the breakableconnecting structure can be made to break upon expansion of the stent,thereby disconnecting the stent sections. As a further option, stent 10may have a structure that enables the delivery of a variety oftherapeutic substances to the body lumen. For example, stent 10 can beconstructed with a mesh or cellular material loaded with one or moretherapeutic substances that are released over time.

FIGS. 2A and 2B are side views of a multi-section stent 50 having abreakable connection structure incorporating square grooves 52, 56, 58,60. Stent 50 substantially conforms to stent 10 of FIGS. 1A-1C, andincludes five stent sections 12, 14, 16, 18, 20. Instead of a v-shapedgroove for each connecting member 34, 36, 38, 40, however, stent 50makes use of square grooves 52, 54 56, 58. Specifically, each groove 52,54, 56, 58 has a substantially square or rectangular cross-section.

As shown in FIG. 2A, each groove 52, 54, 56, 58 extendscircumferentially about stent 50 at a position separating two adjacentstent sections 12, 14, 16, 18, 20. Each groove 52, 54, 56, 58 defines athinned portion of stent 50, weakening the stent to promote breakage. Aswith stent 10, grooves 52, 54, 56, 58 of stent 50 can be supplemented byperforation, scribing, etching, milling, lathing or other processes tofurther weaken the respective connecting member 34, 36, 38, 40.Following breakage of connecting members 34, 36, 38, 40, as shown inFIG. 2B, stent sections 12, 14, 16, 18, 20 are free to move relative toone another within the body lumen.

FIGS. 3A and 3B are side views of a multi-section stent 60 having aseparable connection structure incorporating perforated connectingmembers 34, 36, 38, 40. In the example of FIGS. 3A and 3B, stent 60includes four stent sections 12, 14, 16, 18. Each connecting member 34,36, 38 is integrally formed with the body of stent 60, but incorporate aseries of perforations 62, 64, 66, respectively, that extend about thestent. Each series of perforations 62, 64, 66 defines the junctionbetween adjacent stent sections 12, 14, 16, 18. Perforations 62, 64, 66weaken stent 60 in the vicinity of the junction, promoting breakageunder intraluminal forces.

Perforations 62, 64, 66 can be formed following fabrication of stent 60by a variety of processes and mechanisms such as, e.g., mechanicalneedles or punches, laser ablation, or chemical etching. Alternatively,stent 60 could be molded or laminated to yield perforations 62, 64, 66.In some embodiments, it is conceivable that perforations 62, 64, 66 neednot extend entirely through the wall of stent 60. Instead, partialpenetration of the wall at a series of positions may be sufficient toweaken connecting members 34, 36, 38 for breakage.

FIGS. 4A and 4B are side views of a multi-section stent 68 having aseparable connection structure incorporating sets of discrete breakableconnecting members 70, 72, 74, 76. FIG. 4C is a perspective view ofmulti-section stent 68. As best shown in FIG. 4C, connecting members 70,72, 74, 76 may form rod-like elements distributed about the periphery ofrespective stent sections 12, 14, 16, 18, 20 on a side facing adjacentstent sections. Connecting members 70, 72, 74, 76 bridge adjacent stentsections 12, 14, 16, 18 to connect the stent sections and hold stent 68intact for deployment and positioning within the body lumen.

Each connecting member 70, 72, 74, 76 is manufactured to break underintraluminal forces, however, following deployment of stent 68 withinthe body lumen. For example, each connecting member 70, 72, 74, 76 mayinclude a weakened portion 78 that promotes breakage. As in otherembodiments, weakened portion 78 can be formed by thinning, perforating,or prestressing connecting members 70, 72, 74, 76. Alternatively, stent68 can be molded to form connecting members 70, 72, 74, 76, along withweakened portions 78. Following breakage of connecting members 70, 72,74, 76, stent sections 12, 14, 16, 18, 20 are able to moveindependently, as indicated in FIG. 4B.

Use of rod-like elements as connecting members 70, 72, 74, 76 canprovide the added benefit of stability to stent sections 12, 14, 16, 18.In particular, the rod-like elements extend outward from stent sections12, 14, 16, 18 and can engage the inner wall of the body lumen to resistaxial tumbling of the respective stent section. For added stability,connecting members 70, 72, 74, 76 may take the form of tab-like elementsthat, relative to rod-like elements, exhibit greater lateral surfacearea for contact with the lumen wall. In either case, the resultingconnecting members 70, 72, 74, 76 provide extensions that counteracttumbling forces.

FIGS. 5A and 5B are side views of a multi-section stent 78 having aseparable connection structure incorporating sets of discrete degradableor physically breakable connecting members 80, 82, 84, 86. As in stent68, connecting members 80, 82, 84, 86 may take the form of rod-like, ortab-like elements that bridge a gap between adjacent stent sections 12,14, 16, 18, 20. In the example of FIGS. 5A and 5B, connecting members80, 82, 84, 86 take on a tab-like configuration. Connecting members 80,82, 84, 86 thereby connect stent sections 12, 14, 16, 18, 20 and holdstent 78 intact for deployment and positioning. Each connecting member80, 82, 84, 86 forms two halves, however, that can be held together witha material 90 that can be made from biodegradable or physicallybreakable material.

If made with a biodegradable material, material 90 dissolves orotherwise degrades upon interaction with fluids within the body lumen toa point at which connecting members 80, 82, 84, 86 break apart.Alternatively, if made with a physically breakable material,intraluminal forces cause connecting members 80, 82, 84, 86 to breakapart at material 90. In this case, the biocompatible material formingmaterial 90 could take the form of a briffle material that is notnecessarily degradable, but which readily breaks under intraluminalforces or upon expansion of stent 68. Degradation or physical breakageyields discrete stent sections 12, 14, 16, 18, which then areindependently movable within the body lumen.

In the example of FIGS. 5A and 5B, stent sections 12, 14, 16, 18, 20 canbe fabricated as discrete components, e.g., by molding, machining,lamination, or other techniques, and bonded together using material 90.In this case, discrete stent sections 12, 14, 16, 18, 20 are connectedtogether to form stent 78. Alternatively, stent 78 could be molded as anintegral component, with material 90 being insert molded to connectadjacent connecting members 80, 82, 84, 86. Examples of degradablematerials suitable for use as material 90 include fibrin, collagen,polymers, polyurethane, sugars, polyunhydrides, and polyethyloxides.Degradable materials could be mixed with therapeutic substances, ifdesired, for release into the body lumen upon degradation of material90. Examples of breakable, biocompatible materials that could be used asmaterial 90 include metals such as gold, silver, platinum, stainlesssteel, titanium, tantalum, and Nitinol, as well as any of thebiodegradable materials mentioned above, i.e., fibrin, collagen,polymers, polyurethane, sugars, polyunhydrides, and polyethyloxides.

FIGS. 6A, 6B, and 6C are side views of a multi-section stent 92 having abreakable connection structure incorporating pairs of interlocking links94, 96 that connect adjacent stent sections 12, 14, 16, 18. In theexample of FIGS. 6A, 6B, and 6C, each of stent sections 12, 14, 16, 18takes the form of an interlocking matrix that is woven in a mannersimilar to a chain link fence. Stent sections 12, 14, 16, 18 in thisembodiment can be fabricated from the same materials used for otherembodiments. Again, examples of biocompatible materials that could beused include metals such as gold, silver, platinum, stainless steel,titanium, tantalum, and Nitinol. The matrix can be formed from an arrayof links substantially identical to links 94, 96. The links in each ofstent sections 12, 14, 16, 18 define a ring-like structure. Each oflinks 94, 96 interlocks with a link in one of stent sections 12, 14, 16,18 at one end, and interlocks with one another at the other end, therebyholding the stent sections together to form stent 92. For example, link94 extends from a first stent section 12, whereas link 96 extends from asecond stent section 14. Link pairs 94, 96 can be distributed about thecircumferences of adjacent stent sections 12, 14, 16, 18, holding themat multiple points.

As shown in FIG. 6A, links 94, 96 can be structured to interlock withone another and form an overlap region 100. Similarly, links 94, 96 mayform overlap regions 102, 104 with the stent sections 12, 14, 16, 18with which they interlock. A degradable or physically breakable material98 can be formed in each of overlap regions 100, 102, 104 to fortify theinterlock, and thereby maintain stent sections 12, 14, 16, 18 in asubstantially fixed manner. Thus, the degradable material helps keepmulti-section stent 92 intact for deployment and positioning. Also, thedegradable material 98 prevents longitudinal movement of stent sections12, 14, 16, 18 relative to one another, maintaining the stent sectionsat a predetermined spacing. Following deployment, however, the materialdegrades, relaxing the interlock between links 94, 96, as well as theinterlocks between the links and respective stent sections 12, 14, 16,18.

Upon degradation of the material in overlap regions 100, 102, 104, stentsections 12, 14, 16, 18 remain connected to one another, but are able tomore freely move about the interconnection points. As shown in FIG. 6C,for example, stent sections 12, 14, 16, 18 are able to tilt relative toone another. Notably, in the absence of overlap regions 100, 102, 104,stent sections 12, 14, 16, 18 are able to move longitudinally away fromone another, at least to the extent permitted by the remaining interlockpoints. Consequently, as indicated in both FIG. 6B and FIG. 6C, stent 92is actually capable of expanding its length following deployment. At thesame time, however, the length of stent 92 is constrained by theremaining interconnection of links 92, 94.

FIGS. 7A and 7B are side views of a multi-section stent 106 having abreakable connection structure incorporating alternative interlockinglinks 108. Stent 106 conforms substantially to stent 92 of FIGS. 6A-6C.However, stent 106 makes use of a single link 108, instead of link pairs92, 94, to connect adjacent stent sections 12, 14, 16, 18. Link 108interlocks with adjacent stent sections 12, 14, 16, 18 at opposite ends,forming overlap regions 110, 112 that can be filled with a breakable ordegradable material 113 to fortify the interconnection. As shown in FIG.7B, following degradation of the material, stent sections 12, 14, 16, 18are more freely movable. Moreover, upon elimination of overlap regions110, 112, the length of stent 106 can be expanded.

FIGS. 8A and 8B are side views of a multi-section stent 114 having aspring structure with breakable or degradable spring arms 116. Eachstent section 12, 14, 16 takes the form of a self-expandable spring coilhaving multiple turns 118. Spring arms 120, 122 extend between adjacentstent sections 12, 14, 16 to form connecting members. A biodegradable orbreakable material 124 joins spring arms 120, 122 to hold stent 114together. Alternatively, spring arms 120, 122 may form a continuousmember that is weakened, e.g., by thinning, perforation, etc., topromote breakage under intraluminal forces. Following breakage, as shownin FIG. 8B, stent sections 12, 14, 16 are detached and freely movablerelative to one another.

FIGS. 9A and 9B are perspective side views of a multi-section stent 124having connecting loops 126 that permit movement and flexibility ofstent sections 128, 130, 132 relative to one another. As shown in FIG.9A, each section 128, 130, 132 of stent 124 may take the form of a ring.Adjacent rings 128, 130, 132 are held together by connecting loops 126.Loops 126 can be made from a rigid material and sized to allow playbetween rings 128, 130, 132. In other words, loops 126 can be sized topermit rings 128, 130, 132 to move back and forth in a longitudinal ortilting direction relative to one another. Loops 126 preferably aresized small enough to limit axial tumbling of rings 128, 130, 132 withinthe body lumen. Following deployment, rings 128, 130, 132 are movablerelative to one another. As a further alternative, loops 126 can befabricated from an elastomeric material that allows rings 128, 130, 132.In either case, stent 124 provides flexibility, allowing rings 128, 130,132 to adapt to the body lumen in which the stent is positioned.

FIGS. 10A and 10C are side views of a multi-section stent 134 having aconnecting structure in the form of a degradable housing 136 that bindsstent sections 138, 140, 142, 144 together. FIG. 10B is an end view ofstent 134. Upon deployment, housing 136 is degradable, thereby releasingsections 138, 140, 142, 144, and allowing them to move relative to oneanother. As shown in FIG. 10A, housing 136 may take the form of acontinuous cylinder that is molded or formed from a sheet.Alternatively, housing 136 may be cage- or net-like, having a number ofdifferent threads that cross one another. In either case, housing 136can be formed from any of the biodegradable materials described herein.Following degradation of housing 136, stent sections 138, 140, 142, 144are free to move and adapt to the body lumen in which stent 134 ispositioned.

FIG. 11A is a perspective view of a multi-sectional stent. FIGS. 11B andC are end and enlarged side views of a multi-sectional stent 200. Themulti-sectional stent 200 includes stent sections 205 and a separableconnection structure 210 incorporating four sets of discrete, physicallybreakable connecting members 215 positioned between each pair of stentsection 205. The connecting members 215 take the form of a pairconnected rods 220 and 225 that form an angle, alpha, at their vertex230. The angle alpha can be adjusted to increase the lateral andlongitudinal flexibility of the stent 200. For example, referring toFIGS. 12 and 13, which are a side view of the multi-sectional stent andthe stent deployed in an artery, the angle alpha may be relativelysmall, e.g., less than 45°. Although the stent 200 may include one ormore stent sections 205, for simplicity, only two stent sections areillustrated. In addition, although one or more connecting members 215can be used to connect adjacent stent sections 205, for simplicity onlytwo connecting members are illustrated. A stent as described above willhave good axial flexibility combined with an ability to provide aconcentrated opening force along a relatively short length of an artery235 because the stent sections 205 are deployed close to each other.

Referring to FIGS. 14 and 15, which show a side view of themulti-sectional stent having a relatively large angle and the stentdeployed in an artery, the angle alpha may be relatively large, e.g.,greater than 135°. Such a connecting member configuration will providegood lateral flexibility, i.e., the ability to be delivered throughtortuous vessels, combined with an ability to provide an opening forceseparated over a relatively long length of the artery 235. Referring toFIG. 16, the angle alpha may be in a middle range, i.e., between 45° and135°, such as an angle of 90°. Such a connecting member configurationwill provide moderate lateral flexibility and moderate axial flexibilitycombined with an ability to provide an opening force separated over alength of the artery 235.

The angle alpha can be specified based upon the patient's particularvasculature and the characteristics of the lesion being treated.Moreover, the number of the stent sections 205 can be varied for thesame reasons. For example, referring to FIG. 17, which shows a deployedstent in a tortuous artery, a patient having tortuous arteries withlengthy regions of severe lesions 240 may be treated with multiplemulti-sectional stents 200, each having two stent sections 205 joined byconnecting members 215 having the angle alpha formed relatively small.The stents 200 are deployed adjacent to other stents 200 so thattogether they provide a concentrated opening force in the lumen of theartery 235 along a long length of the artery. The reduced number ofstent sections 205 in each stent 200 improves the ability of acardiologist or radiologist to deploy the stents through and in tortuousvessels. The magnitude of the angle alpha causes the stent sections 205to be closely adjacent to and supportive of the lumen of the artery 234.

Referring to FIG. 18, a patient having less torturous arteries 235 butnonetheless having severe lesions 245 would need an opening forceconcentrated along a considerable length of the artery. The stent 200 totreat such a patient has a greater number of stent section 205 with arelatively small angle alpha. Although not as flexible along its length,the stent 200 can be delivered to the lesions along a greater length ofthe artery 235 than can the stent 200 of FIG. 17.

Modifications can be made to the multi-sectional stent 200 beyond thosedescribed above. For example, referring to FIGS. 19 and 20, the numberand length of the breakable connecting members can be varied.Specifically, referring to FIG. 19, the multi-sectional stent 200includes one connecting member 215 that connects adjacent stent section205. The length of the connecting members 215 can be varied along thelength of the stent 200 to tailor the stent's characteristics, such asflexibility, to a patient's vasculature and disease condition. Referringto FIG. 20, the stent sections 205 are connected by pairs of connectingmembers 215 connected substantially adjacent to each other along thecircumference of the stent section. By connecting the connecting member215 to the stent section 205 in this manner the stent has increasedflexibility because the flex points are close to each other. Such aconfiguration is easily deployed through tortuous vessels.

Although stent 200 is shown above with the connecting members 215attached to adjacent stent section 205 at analogous locations around thecircumference of the adjacent stent sections, the connecting member 215can be attached at offset points around the circumference of the stentsections. For example, as illustrated in FIGS. 21 and 22, the connectingmembers 215 are attached at positions that are approximately 180° offsetalong the circumference of adjacent stent section 205. The connectingmembers 215 may be in the same plane as an outer wall 255 of the stentsections 205. In this configuration, the connecting members 215 curvearound the plane of the circumference of an outer surface 255 of thestent sections 205. The stent 200 of FIG. 21 has two connecting members215 connecting the stent sections 205. The connecting members 215 areeach formed with a pair of angles alpha, and the vertex of each anglebeing closer to the stent sections that shown in the implementationsdescribed above.

In the stent of FIG. 22, the vertex of the angle alpha is centeredbetween the adjacent stent sections 205. Although the connecting member215 is illustrated as encircling approximately 300° of the circumferenceof the stent sections 205, that characteristic can be varied more orless. For example, the connecting member 215 may encircle twocircumferences, i.e., 720°, and have an angle alpha with a vertex formedat a point that is approximately halfway through that 720° encirclement.Such a configuration is very flexible and can be used to connectmultiple stent sections 205 to be placed in a long section of theartery.

The stent 200 may be deployed and positioned in an artery by, forexample, balloon expansion or using the inherent expansion property ofthe material, such as Nitinol, of which the stent sections 205 andconnecting members 215 are constructed. If balloon expansion using aballoon catheter is the method used for delivering the stent 200, thestent first is placed over the balloon so that it can be delivered tothe lesion at which it will be expanded. Because of the wide variationin stent configurations, as described above, a range of balloondiameters and lengths may be used to match the characteristics of thestent to artery in which the stent will be deployed. For example, tostent large arteries a large diameter balloon should be selected toensure that the balloon opens the stent completely. Similarly, if thestent is relatively long, the balloon should have a corresponding lengthto ensure that the entire length of the stent is expanded. Although thestents and balloons may be supplied separately to the physician, amanufacturer may provide a selection of kits containing a combination ofa stent and a properly sized balloon catheter mounted to the stent. Thekit also may contain other devices necessary for the procedure ofdeploying the stent, such as an introducer, guide wire, scalpel, andsutures.

If the stent is made of a material with shape memory characteristics,such as Nitinol, the stent may be deployed on a catheter and surroundedby a sheath that prevents the stent from expanding. When the stent ispositioned in the lumen of the artery adjacent to the lesion, the sheathis removed and the stent expands to open the lumen of the artery.Because of the wide variation in stent configuration, a range of sheathsmay be available for matching with the particular stent.

Referring to FIGS. 23 and 24, a catheter 300 for delivering a stent madeof a shape memory metal includes a sheath 305 for surrounding the stentto be delivered. The sheath 305 includes a first diameter section 310and a second diameter section 315. The stent is surrounded by the seconddiameter section 315, which, as illustrated, has a greater innerdiameter than does the first diameter section 310. A shoulder 320defined at the intersection of the two sections 310, 315 prevents thestent 300 from sliding proximally along the catheter 300. As illustratedin FIG. 23, the length of the second section 315 can be relatively long,or, as illustrated in FIG. 24, relatively short. Other variations in therelative length of the sections 310, 315 are possible and may beselected based on the configuration of the stent 200 and the vasculaturein which the stent will be deployed and positioned.

When the stent 200 is deployed in an artery, the connecting members 215may physically separate from one of the adjacent stent sections 205. Thephysical separation also may occur at a later time by enzymatic action,dissolution of a coating on the connecting member, the pulsatilemovement and forces imparted by the artery surrounding the stentsections, or one of the other means described above. To control thephysical separation more predictably, the connecting member 215 may beweakened so that it will break preferentially at a particular location,for example, at the vertex of the angle alpha of the two rods 220, 225,or at their connections to the stent sections 205. The force exerted onthe stent when it is expanded by the balloon, or by the stent itselfwhen it expands due to shape memory properties, may be sufficient tocause the connecting members 215 to break from the stent sections.Referring to the stent 200 of FIGS. 21 and 22, the attachment of theconnecting members 215 to the stent sections 205 will be stressed as thestent sections 205 expand or are expanded because the attachments are onopposite sides of the expanding circumferences of the adjacent stentsections 205. Accordingly, in this configuration, the stent sections arephysically separated during the deployment of the stent.

In the above configurations, the separated connecting member 215 has anend that is separated from a stent section 205, or the rods 220 and 225each have an end that is separated from the respective adjacent rod 225,220. The end, which may be in contact with the inner wall, or intima, ofthe artery may be formed so that it is smooth or has minimally sharpedges that may otherwise irritate the intima. The end of the connectingmember to be separated may be weakened, as described above, and thenpolished around the weakened portion to smooth any rough or sharp edges.Nonetheless, even if there is a sharp edge remaining after separation,scar tissue will form around the separated connecting member andencapsulate the sharp edge. To encourage tissue formation on thesurfaces of the connecting members and stent sections, if desired, thesurfaces of those components may be textured to encourage tissuein-growth and the formation of a stable layer of tissue on the surfaces.

The separated connecting members 215 can provide a stabilizing functionfor the separated stent sections by acting as leverage against tumbling.Referring to FIGS. 25-27, the stent sections 205 can be separated fromthe connecting members 215 in a variety of configurations that provideleverage to prevent the stent sections from tumbling within the artery.Each stent section 205, as shown in FIG. 25, may have two attachedconnecting members 215 that function in combination to prevent tumblingand to stabilize the orientation of the stent section 205. Theconnecting members 215 are co-planar and follow the circumference of theouter surface 255 of the stent section 205, or are close to beingcoplanar to the outer surface 255 of the stent section. As the length ofthe connecting members 215 or the stent sections 205 are increased, andas the distance that the connecting member extends away from the stentsection is increased, the likelihood of tumbling is reduced.

The stent sections 205 shown in FIG. 26 are not necessarily co-planarwith the connecting members 215 and in contact with the intimal layer ofthe artery, which would have a tendency to prevent tumbling.Nonetheless, each connecting member has two potential points of contact340, 345 with the arterial wall to prevent tumbling. One point 345 ofthe connecting member prevents clockwise tumbling and the other point340 prevents counter-clockwise tumbling. The stent 200 of FIG. 26 can bemodified to have a single connecting member 215 attached and stillrestrict any tendency of the stent section 205 to tumble.

The stent section 205 shown in FIG. 27 is separated from the adjacentstent sections 205 by breaking or separating two connecting members 215at the vertex of the angle alpha. Like the stent sections of FIG. 26,two points 350 prevent clockwise tumbling and two different points 355prevent counter-clockwise tumbling.

These stents can be fabricated using the materials and methods for thevarious stents described above. In addition, these stents can befabricated using electron discharge machining (“EDM”). For example, asillustrated in FIGS. 28-31, a tube 400 has a series of slots 405 cutthrough an outer wall 410. When the series of slots 405 are cut and thecut wall sections are removed, a stent 415 with a connecting member 420results. Additionally, the stent can have grooves 425 cut into theconnecting member 420 to weaken the member so that it willpreferentially separate at the predetermined grooves 425. A number ofembodiments of the present invention have been described. Nevertheless,it will be understood that various modifications may be made withoutdeparting from the spirit and scope of the invention. Accordingly, otherembodiments are within the scope of the following claims.

What is claimed is:
 1. A stent comprising: a first stent section; asecond stent section; and at least one connecting member having a firstend attached to the first stent section, a second end attached to thesecond stent section and a physically separable portion.
 2. The stent ofclaim 1, wherein the physically separable portion comprises at least onegroove in the connecting member.
 3. The stent of claim 2, wherein thegroove is formed adjacent to the first end.
 4. The stent of claim 2,wherein grooves are formed adjacent to the first end and the second end.5. The stent of claim 1, wherein the connecting member further includesan angled portion including an angle.
 6. The stent of claim 5, whereinthe angled portion includes a groove and the physically separableportion comprises the groove.
 7. The stent of claim 5, wherein the angleis less than 45°.
 8. The stent of claim 5, wherein the angle is between45° and 135°.
 9. The stent of claim 5, wherein the angle is between 135°and 180°.
 10. The stent of claim 1, wherein the stent includes fourconnecting members.
 11. The stent of claim 1, wherein the stent includestwo connecting members.
 12. The stent of claim 1, wherein eachconnecting member includes a first end attached to the first stentsection and a second end attached to the second stent section and thefirst end of the first stent is adjacent to the first end of the secondstent.
 13. The stent of claim 12, wherein the first end of the firstconnecting member and the first end of the second connecting member areseparated by approximately 180°.
 14. The stent of claim 13, wherein thesecond end of the first connecting member and the second end of thesecond connecting member are separated by approximately 180°.
 15. Thestent of claim 1, wherein the physically separable portion separatesduring a deployment of the stent.
 16. The stent of claim 1, wherein thephysically separable portion separates after a deployment of the stent.17. The stent of claim 1, wherein the stent sections comprise a shapememory material.
 18. A stent comprising: a first stent section; a secondstent section; and a pair of connecting members positioned between thestent sections and connecting the stent sections, wherein eachconnecting member is substantially co-planar over a portion of a lengthof the connecting member with the at least one stent section andincludes a first end attached to the first stent section, a second endattached to the second stent section and a physically separable portion.19. The stent of claim 18, wherein the physically separable portion of afirst connecting member is configured to separate from the first stentsection and the physically separable portion of the second connectingmember is configured to separate from the second stent section, wherebythe first connecting member is configured to reduce tumbling of thefirst stent section and the second connecting member is configured toreduce tumbling of the second stent section.
 20. The stent of claim 18,wherein the stent is fabricated by electron discharge machining.